For a long time, follicle-stimulating hormone (FSH) was used as a marker of ovarian reserve, but it has since been largely replaced by anti-Müllerian hormone (AMH), which is considered more reliable.  

However, an FSH level above 15 IU/L at the beginning of the cycle is associated with:  

- Lower success rates in assisted reproduction (ART).  

- Weaker response to ovarian stimulation, leading to fewer retrieved eggs and fewer embryos available for transfer.  

A high FSH level is therefore a sign of a poorer prognosis. But this test has limitations because it does not assess egg quality. For this reason, FSH is rarely used today to exclude women from ART programs.